Field of the Invention
The present invention relates to a mechanism for conducting a discovery of small cells or secondary cells located in a macro cell or primary cell. In particular, the present invention is directed to apparatuses, methods and computer program products by means of which the discovery of small cells in a macro cell by a user equipment can be improved.
Related Background Art
Prior art which is related to this technical field can e.g. be found in technical specifications according to 3GPP TS 36.211 (e.g. version 10.5.0).
The following meanings for the abbreviations used in this specification apply:    BS: base station    BW: bandwidth    CA: carrier aggregation    CDM: code division multiplex    CPU: central processing unit    CRS common reference signal    DL: downlink    eNB: evolved node B    FDM: frequency division multiplex    ID: identification    LTE: Long Term Evolution    LTE-A: LTE Advanced    OTDOA: observed time difference of arrival    PCFICH: physical control format indicator channel    PCell: primary cell    PCI: physical cell identifier    PDCCH: physical downlink control channel    PDCH: physical discovery channel    PDSCH: physical downlink shared channel    PRACH: physical random access channel    PRB: physical resource block    PRS: position reference signal    PSS: primary synchronization signal    RRH: radio remote head    RS: reference signal    RSTD: reference signal time difference    SCell: secondary cell    SINR: signal to interference plus noise ration    SSS: secondary synchronization signal    UE: user equipment    UL: uplink
In the last years, an increasing extension of communication networks, e.g. of wire based communication networks, such as the Integrated Services Digital Network (ISDN), DSL, or wireless communication networks, such as the cdma2000 (code division multiple access) system, cellular 3rd generation (3G) communication networks like the Universal Mobile Telecommunications System (UMTS), enhanced communication networks based e.g. on LTE, cellular 2nd generation (2G) communication networks like the Global System for Mobile communications (GSM), the General Packet Radio System (GPRS), the Enhanced Data Rates for Global Evolutions (EDGE), or other wireless communication system, such as the Wireless Local Area Network (WLAN), Bluetooth or Worldwide Interoperability for Microwave Access (WiMAX), took place all over the world. Various organizations, such as the 3rd Generation Partnership Project (3GPP), Telecoms & Internet converged Services & Protocols for Advanced Networks (TISPAN), the International Telecommunication Union (ITU), 3rd Generation Partnership Project 2 (3GPP2), Internet Engineering Task Force (IETF), the IEEE (Institute of Electrical and Electronics Engineers), the WiMAX Forum and the like are working on standards for telecommunication network and access environments.
For improving the performance of new communication networks, such as that of LTE or LTE-A based networks, carrier aggregation (CA) is employed so as to support wider transmission bandwidths. CA in LTE-A extends the maximum bandwidth in the UL or DL directions by aggregating multiple carriers within a frequency band (intra-band CA) or across frequency bands (inter-band CA).
In order to support all CA deployment scenarios, it is contemplated to design an additional carrier type. Such a new carrier type does not need to be backward compatible and allows thus a certain flexibility in its configuration. In other words, as such a new type of carrier does not necessarily be usable by legacy UE, some enhancement may be supported on it, for example a reduction of the density or even a re-design of reference signals which may allow to save overhead, and to consider some optimization to suit to specific application scenarios.
A further item of new communication network system is the implementation of heterogeneous networks consisting of e.g. a “normal” communication cell (referred to as macro cell) and plural small cells which allows a better coverage and possibly outsourcing options from a communication to the macro cell to a small cell (which may be connected to the network e.g. by a backhaul network offering higher capacity), or the like. In the following, it is assumed that a macro cell is used as a primary cell (PCell) for a UE communication, and the small cells are used as secondary cells (SCells) for the UE communication.
In order to enhance the usage of heterogeneous networks, i.e. to achieve heterogeneous network mobility enhancements for e.g. LTE based networks, it is necessary to provide suitable mechanisms for small cell discovery/identification. In this context, it is considered to use also the new carrier type for a quick cell identification of small cells, for example in a scenario where the small cells are constituted by using RRHs.
An example for a new physical channel is the so-called Physical Discovery Channel (PDCH). The PDCH is configured such that is has a relative long periodicity, e.g. a few seconds assuming relaxed measurement requirements for energy saving and low mobility and sufficient time/frequency radio resource density for one-shot PDCH reception by the UE for efficient UE battery consumption (e.g. full use of a few subframes).
However, due to the long periodicity of PDCH, it may introduce larger cell access/detection delay. An attempt to solve this by, for example, a simple reduction of the periodicity may not be feasible as the other advantages of PDCH, such as low power consumption, would be affected thereby.